For an Organic Light-Emitting Diode (OLED) product, a film-forming method mainly includes evaporation and ink-jet printing. The latter has attracted more and more attentions by manufacturers due to such advantages as shorter tact time and fewer desired materials. Similar to a traditional dot matrix printer, an ink-jet printing device may print an OLED material onto a back plate through a printing head. However, in use, the printing head may be contaminated or a droplet of the OLED material may be attached onto a surface of the printing head, so a surface performance of the printing head may be degraded. In this regard, the spraying of a droplet of a film-forming material from a nozzle in the printing head may be adversely affected, and an overall characteristic of the droplet may be changed. To be specific, the droplet may be fallen onto the back plate at a wrong position, or a satellite droplet may occur (i.e., a small portion of the entire droplet may be fallen onto the back plate outside a desired position), or the droplet on the back plate may become fuzzy. In addition, before the use, it is required to align the printing head. In the case that there is a contaminant particle on the nozzle, the droplet of the film-forming material may not be fallen onto the back plate at the desired position after the alignment.
In order to prevent a spraying effect of the film-forming material from being adversely affected by the contaminated nozzle, one effective method is to clean the printing head and the nozzle. In the related art, a method for cleaning the nozzle of the printing head mainly includes spraying the film-forming material, e.g., the OLED material, for the ink-jet printing through the printing head so as to remove the contaminant, and then wiping the nozzle with a cleaning fabric. However, in the case of wiping the nozzle of the printing head with the cleaning fabric, the nozzle may be damaged. In addition, some other matters may also be attached onto the cleaning fabric, and during the wiping, fibers of the cleaning fabric may also be attached onto the nozzle, resulting in secondary contamination. Hence, it is unnecessary to essentially improve the spraying effect of the nozzle.